1. Field of the Invention
The present invention relates to a circuit device and an inkjet head assembly, and more particularly relates to a technology for protecting an electrical wiring pattern on a circuit board.
2. Description of the Related Art
There is known a circuit board configured to include a base material, such as a resin film and glass epoxy, a thin film made of a metallic material, such as copper, formed on the base material, an electrical wiring pattern formed by patterning the metal film by etching or other methods, and further a coating made of an insulating material, such as a solder resist, for coating the electrical wiring pattern.
The circuit board is widely used in industrial equipment and/or consumer equipment. Thus, as the circuit board is used in various applications and environments, the use environments of the circuit board are assumed to include a high-humidity environment, a high-temperature environment, and an environment where foreign materials, such as powder dust, are present.
Such environments may cause a problem of a short circuit or an open circuit between electrical wirings due to degradation of insulating materials and a problem of a short circuit of the electrical wiring caused by water and foreign materials intruding in between an insulating layer and a base material.
In general, when the circuit board is used in the high-humidity environment and the environment involving a large amount of foreign materials (materials having conductivity in particular), long-term reliability (resistance) becomes an issue. Since an electrical wiring pattern is coated with an insulating material in order to prevent a short circuit and an open circuit of the electrical wiring pattern, the reliability is not an issue in a short term use. However, in the case where the circuit board is used over a long period of time, further measures need to be taken in a viewpoint of assuring long-term reliability.
Described in Japanese Patent Application Laid-Open No. 2010-86992 is a board having conductive patterns formed thereon and a semiconductor element mounted thereon, in which a semiconductor element mounting surface of the board is coated with sealing resin, and the surface of a coating film (solder resist film) for coating the conductive patterns is coated with a glass film.
Such configuration suppresses an intrusion of water into the coating layer and prevents a short circuit between the conductive patterns.